The invention relates to a diagnostic function for an internal-combustion engine whose power is adjusted by a power-determining signal. For this purpose, a determination unit determines a first signal based on a desired-value definition, and a torque controller determines a second signal from an engine torque. A selection device then sets either the determination device or the torque controller to be dominant for the power determining signal.
German Patent Document DE 19953767.4, (not prior art) discloses a control circuit structure having the above-mentioned construction, in which the determination device corresponds, for example, to the rotational speed controller. The rotational speed controller determines the first signal (for example, a first injection quantity) based on the desired rotational speed value definition. A torque controller determines a second signal (for example, a second injection quantity) from the engine torque and a maximum permissible torque. The selection device then sets as dominant, the controller whose calculated injection quantity is lowest. In this manner the internal-combustion engine is effectively protected from being overloaded. However, an error in the torque detection or calculation is not yet taken into account in the case of this control circuit structure.
One object of the present invention is to provide a control system that includes a failure prevention device.
This and other objects and advantages are achieved by the method and apparatus according to the invention, in which an error mode is set when values of the engine torque are not plausible. With the setting of the error mode, if the determination unit is then currently dominant, the dominance is maintained. On the other hand, when the torque controller is dominant, a change of dominance will then be carried out.
According to an embodiment of the invention, the change of dominance takes place after a transition function. As a further feature, the engine torque is controlled from the last plausible value to zero or, alternatively the second signal is controlled from the last value to a high value.
The method and apparatus according to the invention and further developments thereof offer the advantage that a failure in the torque detection will not result in an uncontrolled behavior of the internal-combustion engine. In other words, even when the torque detection fails, a reduced normal operation of the internal-combustion engine will be ensured continuing computation of the power-determining signal. Introduction of the transition function prevents a jump in the power-determining signal during a change in dominance. A power-determining signal in the sense of the invention is an injection quantity or a control path of a control rod.
Another protective measure of the internal-combustion engine in the event of a failure of the torque detection lies in using the diagnostic function adapting a limit value curve of the maximum permissible first signal. This limit value curve is adapted to the lower values of the first signal. The internal-combustion engine is thereby operated at a safe power level in that, for example, the injection quantity is reduced.
A corresponding return function within the diagnostic function reacts to sporadically occurring errors in the torque detection. As soon as plausible torque values are present again and a time period has elapsed, the return will take place to the normal function.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.